The study was conducted using the specimens obtained from 110 patients that have applied to Training and Research Hospital. Rapid detection of SARS-CoV-2 was performed using RT-PCR test. Articles about antibody response after SARS-CoV-2 infection are limited in number. There are scarcely any studies because the antibodies in immunoassay systems have become available very recently. Roche SARS-CoV-2 antibody test identifies total antibody levels but does not differentiate virus-specific IgM and IgG.
Zhao et al. 18 conducted a study in 173 patients and detected overall seroconversion rate to be 93.1%, whereas seroconversion rate was 82.7% for IgM and 64.7% for IgG. They reported that not analyzing the specimens in the late phases of the disease might be the reason for antibody negativity in 12 patients. In the present study, antibody positivity rate was 20.37% (11/54) in the patient specimens sent from the polyclinic and 57.14% (32/56) in the patient specimens sent from the service/intensive care unit.
Wang et al. 19 detected a positivity rate of 63% for SARS-CoV-2 RNA in the nasopharyngeal smear specimens and 32% in the oropharyngeal smear specimens. RT-PCR was found positive in 86 (78.18%) of the 110 patient specimens sent both from the polyclinic and from the service/intensive care unit. All of the specimens in the present study were obtained by nasopharyngeal smear, and the positivity rate was quite high.
SARS CoV 2 RT-PCR test was negative in 11 of the 43 patients with positive Roche Anti SARS CoV 2 antibody; 4 of these 11 specimens were from the service, 2 were from the intensive care unit and 5 were from the polyclinic. Antibody seropositivity and PCR negativity in the service/intensive care patients can be attributed to the specimen-associated positivity rates or time of sampling. Accordingly, using antibody test in symptomatic patients with negative RT-PCR can be beneficial in identifying the ill subjects.
Long et al. 5 detected RT–PCR positivity and virus-specific IgM and/or IgG seropositivity in 16 specimens (of which three were asymptomatic) obtained from 164 close contacts; however, they detected RT-PCR negativity and virus-specific IgM and/or IgG seropositivity in the specimens of the 7 of 148 asymptomatic subjects. The fact that the antibody was positive in PCR-negative 5 subjects from the polyclinic indicates that antibody testing can be used during pandemic for not missing the cases and taking necessary isolation measures. Furthermore, antibody tests may help with diagnosis since the RT-PCR-negative symptomatic patients with low viral burden might be overlooked.
Guo et al. 6 conducted a study using 208 plasma specimens (a total of 140 subjects; 82 confirmed and 58 PCR-negative but symptomatic) and they reported that the efficacy of IgM ELISA was higher than that of the PCR after 5.5 days of symptom onset and that combination of IgM ELISA with PCR significantly increased the rate of detecting positivity (98.6%) as compared to PCR alone (51.9%). In addition, many studies have emphasized that serological tests may enhance the rate of positivity and they need to be used in subclinical patients and in the future epidemiologic studies 20-22. In the present study, there were 11 antibody-positive patient specimens (RT-PCR negative) and 86 RT-PCR-positive patient specimens. The rate of detecting Covid-19 positivity was 88.18% (97/110) with combination of antibody and PCR tests.
Rapid viral replication and release of strong proinflammatory cytokines in the early phases of COVID-19 infection may later result in extensive endothelial inflammation and further release of various inflammatory cytokines due to viral infection of the endothelial cell in addition to pulmonary infiltration and extensive alveolar injury 23,24. Neutrophils and leukocytes may strengthen extra-lymphocyte cytokine storm in COVID-19 25. Güçlü et al. found that leukocyte and neutrophil counts were higher but lymphocyte count was lower in severe cases vs. mild cases at hospital admission and that leukocyte and neutrophil counts increase more in severe cases but decrease in mild cases on the third day of hospital stay. However, although lymphocyte count decreased much more in severe cases vs. mild cases on the third day, they reported that the difference is not significant 23. In the present study, leukocyte, neutrophil and erythrocyte counts, hemoglobin, ferritin, CRP, PCT and D- dimer levels were statistically significantly different between the patient specimens sent from the polyclinic and those sent from the service/intensive care unit (p= 0.001, 0.007, 0.002, 0.001, <0.001, 0.012, 0.006 and 0.001, respectively). However, lymphocyte and thrombocyte counts were not statistically significantly different between the patient specimens sent from the polyclinic and sent from the service/intensive care unit (p>0.05).
Some studies detected a relationship between thrombocytopenia and the severity of COVID-19 and related deaths, and it was reported that mortality rate increases as the thrombocyte count decreases 26,27. In the present study, thrombocyte count was significantly low in two (89 and 94, respectively) of the 11 male patients died of COVID-19. Mechanisms associated with the thrombocytes in SARS CoV 2 and the relation with gender could be the subjects of investigation.
Many laboratory parameters make it possible to assess the severity of the disease due to Covid 19 and to predict the risk of progression to serious diseases. In COVID-19 patients, recommendations have been made to establish certain threshold-values for Ferritin, PCT, CRP, D dimer, WBC, NEU, LYM and some other parameters and to evaluate accordingly 28-30. It was found that higher PCT values were associated with disease severity in COVID-19 patients 30 and higher D-dimer values at hospital admission were significantly associated with in-hospital mortality 31. A significant decrease was found in WBC and also other leukocyte formula parameters (neutrophils, eosinophils, basophils, lymphocytes and monocytes) in Covid 19 patients 28. In another study, lymphopenia (83.2%), thrombocytopenia (36.2%) and an increase in D dimer (43.2%) values were observed in COVID-19 patients (32).
It is demonstrated that Covid 19 patients have neutrophilia, leukocytosis and increased procalcitonin due to bacterial (super) infection, thrombocytopenia due to consumption (disseminated) coagulopathy, lymphopenia due to decreased immunological response to the virus, increased CRP levels due to severe viral infection/viremia/viral sepsis, blood coagulation activation and/or severe coagulopathy due to increased D-dimer levels 29. It has been reported that high ferritin levels are associated with acute respiratory distress syndrome (ARDS) and a high risk of death 33. Similar to the studies, it can be said that the significant increase in WBC, NEU PCT, CRP, D dimer, ferritin levels in our study, especially in service/intensive care patients, is due to the increase in the severity of the disease and the occurrence of secondary infections.
In conclusion, it can be suggested that seroprevalence needs to be detected, antibody levels should be determined before vaccination, and antibody should be studied in RT-PCR-negative symptomatic patients because of increasing number of exposure to SARS CoV 2.
Acknowledgments
The authors thank to Diyar-Med Health Products Ind. and Com. Ltd. Co. for supplying Roche SARS-CoV2 antibody test kit.